If memory serves me correct, Scout Starships have tachyon beam emission as well (ie, can decloak enemy ships).
Slightly offtopic, 'Frontline Scouts' is a good role for Scout Starships. They're tough, so they take a pounding through blockaded wormholes, they decloak mines so your attacking fleet doesn't run into them, and as scouts they're cloaked and provide planetary summary information on enemy planets.
There's a bit of an art form to properly using scout starships, and even then they're not a commonly used ship. They're also a bit of an investment in the early game. That said, they're a great way to help decloak mines so your Cleanup Drones can get rid of them, as their toughness means they'll hang around longer than a tachyon drone.